Physical mechanisms driving mesendoderm collective cell migration

One of the main features of life is movement, either as a single entity or in groups. Collective cell migration is characterized
as the behaviour of a group of cells which moves together more efficiently than its components in isolation. It is a fundamental process seen in all multicellular animals and is essential for physiological functions such as wound healing and immune cell surveillance in adults. During embryonic development, collective cell migration is a hallmark of cellular rearrangements and ensures accurate formation of organs and tissues. Invading and metastatic cancer cells can also migrate as collectives thus making this process highly relevant during cancer metastasis.

The mechanisms guiding collectively migrating cells vary and can depend on inherent cellular reorganisation events such as establishment of leader and follower (trailing) cells and on external signals from the microenvironment which act as guidance cues ("inputs"), ultimately generating a collective response for directional migration. The cells in the collective respond to and communicate with each other through biochemical and physical interactions enabled by cell-cell connections (adhesions), thereby coordinating efficient movement. Guidance as well as the intercellular communication can be mediated through physical/mechanical, chemical and/or electrical cues. Extensive studies have revealed the role of major signalling molecules (chemokines) in collective migration. However, recent findings emphasise that mechanical stimuli (pulling, pushing, shear) and physical properties of the surrounding may be equally important for cell migration. Yet, our knowledge of how these physical factors contribute to collective cell migration within living organisms and the underlying mechanisms remain very limited.

The zebrafish embryo constitutes an ideal model organism to study cell migration, as the embryos are transparent and perfectly suited for live cell imaging. Furthermore, it is a highly accessible system where specific cells can be transferred between different embryos (transplantations) or isolated from the embryo for ex vivo experiments. We will focus our research on the mesendoderm tissue, which is a cell collective that is highly conserved in vertebrates and is fundamental for early embryonic development. Mesendoderm cells migrate as a collective along the future head-tail body axis of the embryo and failure in precise collective migration results in embryonic defects in eye and brain and body axis malformations leading to organ degeneration or early embryonic death.

To address the physical basis of mesendoderm collective migration, we will use a highly interdisciplinary approach combining methods and tools from biology, physics and theoretical modelling. We will identify mechanical cues and physical properties of the microenvironment that influence collective migration, and investigate how these signals are transduced through the collective. We will further study how physical barriers and adhesive surfaces contribute to cell migration. Finally, a mathematical model will be developed that aims to recapitulate polarization and directional movements of a collective based on the minimal essential physical parameters.

In summary, the outcomes of the proposed research will have significant impact on our understanding of physical mechanisms that drive collective cell migration of mesendoderm cells in the embryo. This will be essential in expanding our knowledge of embryonic development and will also serve as a framework to understand behaviours of other collectively moving systems in physiological and pathological contexts.

Collective cell migration is an essential process during the formation of functional organs and tissues in all developing embryos. Yet, remarkably little is known about the mechanical guidance cues and physical principles underlying collective cell migration during early embryonic development.

The axial mesendoderm tissue is highly conserved throughout vertebrates and essential during gastrulation for embryonic axes formation and development of the future brain. The anterior part of the mesendoderm collective, the prechordal plate (ppl), consists of a highly motile group of mesenchymal cells that migrate along the future anterior-posterior axis with high directionality towards the animal pole of the embryo.

The overall goal of this proposal is to unravel the physical mechanisms that regulate mesendoderm polarisation and migration during gastrulation. To address this, we will use a highly interdisciplinary approach including molecular, cell and developmental biology methods, biophysical tools and mathematical modelling.
Based on our recent observations that ppl cells physically interact with the moving neighbouring neuroectoderm cells, we will first explore whether external mechanical forces may be sufficient to polarize ppl cells. We will further investigate molecular mechanisms of how these forces can be transduced through the collective for polarization and directed migration. We also aim to identify how permissive physical signals from the environment including mechanical constraints and physical properties of the underlying substrate regulates ppl collective cell migration. Alongside, we will construct a parametrised in silico model that will explain polarization and collective motion and aims to identify the minimal required physical parameters.

Taken together, our integrated approach will reveal novel functions of physical determinants for collective cell migration that will be significant to understand behaviours of other cell collective systems.

- Beneficiaries within the commercial private sector

The project will deliver two aspects with potential link to industry and commercial applications:
1) For the proposed work, we will fabricate a new generation of a fully software-controllable microplate confiner/shearer. This device will enable placement of cells/tissues, confinement and application of forces like compression and shear forces. The first-time fabrication of such a device has potential implications for patent development and commercial exploitation through suppliers for cell manipulation tools.
2) For some aspects of this project, we will work together with engineers from the Warwick Manufacturing Group (WMG), in particular with Dr. Jerome Charmet, who is a specialist in microfabrication of soft lithography devices and micropatterning. As part of this partnership, we have recently approached a company that is interested in commercialisation of such devices.
These potential links with industry will be explored after successful testing of prototypes.

- Beneficiaries within the public sector, third sector or any others

1) The public sector will profit from our research given the impact of our research findings on prevalent diseases related to cancer invasion and metastasis. Better insight into the molecular, cellular and physical mechanisms of cell migration will facilitate development of novel diagnostic approaches and potential new treatment strategies. To improve the healthcare sector, we will seek out collaborations with cancer clinicians at the neighbouring Clinical Trials Unit (CTU).
2) Businesses, industrial and public sectors that recruit scientifically trained staff will profit from training of personnel during this project. In particular, the PDRA supported by this grant will improve their training, including transferable skills such as project and lab management abilities. Additionally, undergraduate and summer students that might be involved in some aspects of this project will also be trained in research design and experimental work. Hence this grant will contribute towards health of UK science and higher education through generating highly trained and skilled researchers.

- Beneficiaries within the wider public

One of CMCB and QBP's missions is to actively participate in public engagement to enable flow of information and knowledge gained from our research to anyone outside academia. Researchers part of this grant will use these platforms to communicate our science and to foster open discussions with the wider public about the importance of our research for normal embryonic development including humans, and for studying diseases such as cancer and metastasis.

We aim to do this through following activities:
1) Programmes and Initiatives - The CMCB and QBP offer high-quality undergraduate programmes that are promoted through informative open days at University and visits to schools and communities. These events are usually well received by prospective future students, but also by the wider audience who will benefit by open discussions with scientists. This includes the recently developed Integrative Science (MSci) Programme, where we will actively participate and communicate our science.
2) Public engagement - We will commit to public engagement events for a broad audience. QBP frequently offers "Public Science Evenings", which are open events at the University, where QBP researchers talk about their work in simple and accessible terms. We will also present our research at the annual "British Science Festival" and the "Summer Science Exhibition" by delivering presentations and engaging activities for the whole family (falling dominos as toy model for force transduction). Researchers involved in this grant will also participate in "Open Campus Days" at the University, where we will showcase fluorescently labelled migrating cells in live zebrafish embryos under the microscope.